Microstructure evolution and mechanical behavior of α/β alternative Mg–Li alloy composite sheets with different initial thickness ratios prepared by accumulative roll bonding

α/β alternative Mg–Li composite sheets with different initial thickness ratio of α to β (H) were prepared by accumulative roll-bonding (ARB). The hard layer necking, microstructure evolution and the strain hardening sequence of the α/β alloys in the composite sheets during the ARB process were studied by optical microscopy (OM), transmission electron microscopy (TEM), X-ray diffraction (XRD), microhardness and tensile test. The results showed that, with the increase of H, the necking of the LA51 layer was relieved, and the grains of the two alloys were gradually refined. With the increase of ARB passes and H, the strength of the composite sheets increased first and then decreased, and the plasticity decreased first and then increased. When H = 1, the ARB3 composite sheet possesses the ultimate tensile strength (UTS), yield strength (YS) and elongation (EL) of 286 ± 1 MPa, 262 ± 6 MPa and 6.4 ± 0.1%, respectively. During the ARB process, the work hardening of the LA141 layer first increased, then that of the LA51 layer increased gradually, and finally that of the two alloy layers increased simultaneously.